This invention relates to a vacuum pump, such as a two-shaft vacuum pump which has an evacuation chamber and, arranged laterally thereto, has at least one oil containing gear chamber which is coupled with an evacuating device and further has a partition situated between the evacuation chamber and the gear chamber. The partition supports bearings for the shafts of the lobe-like rotary impellers situated in the evacuation chamber and labyrinth seals which are situated between the evacuation chamber and the gear chamber and which cooperate with the shafts passing through the partition.
A two-shaft vacuum pump is typically represented by a rotary blower pump (Roats pump) such as disclosed, for example in German Patent No. 1,939,717. It comprises an evacuation chamber in which cooperating lobe-like impellers rotate in rolling contact with one another. In lateral partitions the shafts of the impellers are supported such that they project into laterally adjacent gear chambers where the shafts carry meshing gears which ensure the correct position of the impellers with respect to one another. One of the shafts is coupled with the shaft of a drive motor. As a rule, rotary blower pumps of this type are provided with two gear chambers, but in case of a floating support of the impellers, only a single gear chamber is needed.
The gear chambers which communicate with one another and which are arranged laterally of the evacuation chamber, contain oil which serves for lubricating the gears and the shaft bearings. In order to prevent oil or oil vapors from penetrating into the evacuation chamber, seals are provided on the shafts in the zone of the partitions. The seals may be oil seal rings which are disadvantageous since they are exposed to wear and thus have only a limited service life. Accordingly, instead of oil seal rings, wear-free labyrinth seals are conventionally used.
Two-shaft vacuum pumps, particularly pumps having rotary lobe-like impellers are frequently used in cases where a strictly oil-free evacuation or conveyance of gas has to be ensured. In order to meet this requirement with the simultaneous use of wear-free labyrinth seals, it has been proposed to evacuate the gear chambers to a pressure and maintain such a pressure which is less than the lowest pressure in the evacuation chamber. In this manner, in the zone of the labyrinth seal, a gas flow is generated from the evacuation chamber towards the gear chamber which prevents oil from penetrating in the opposite direction. The higher the volume flow through the labyrinth seal the better the sealing effect.
Since in the gear chambers the oil is swirled (thrown) around by means of a spraying disc in order to lubricate the gears to a sufficient extent, the evacuated gas is significantly enriched with oil. Particularly in case a high volume flow is to be obtained in the zone of the labyrinth seals by means of an evacuation of the gear chambers with a high suction capacity, the quantities of oil entrained from the gear chamber may be large enough to cause the oil level to drop below a minimum limit value. As a result, a satisfactory lubrication of the gears and bearings is no longer ensured.